This invention relates to a hydraulically driven piston pump and nozzle assembly for a high pressure fuel injection system of an internal combustion engine.
A fuel injection system with a pump/nozzle assembly is already known in which fuel which drives the hydraulic piston pump and is under servo pressure is conducted into the spring chamber and functions as a hydraulic spring. The effect of this aforementioned hydraulic spring can be varied by regulating the servo pressure. However, the opening as well as the closing pressure are both thereby varied in a disadvantageous manner and to the same extent.
In modern, high-powered Diesel engines, however, extremely short injection times are required for maximum performance. Furthermore, fuel injection operation must be terminated suddenly and very abruptly, if possible, within one degree of crankshaft rotation, because a delayed termination of the injection of fuel and the after-injections which frequently occur when special provisions are not available unfavorably and detrimentally influence combustion and lead to an elevated emission of hydrocarbons and carbon dioxide from the exhaust manifold. This requirement was partially satisfied in a different known fuel injection system of the basic design, where the pressure exerted on the valve needle is drawn from the controlled servo pressure chamber above the servo piston which drives the pump piston and is conducted into a pressure chamber which acts upon the valve needle. In this system, the elevation of the closing pressure is linked with the course taken by the servo pressure and is also limited by the maximum level for the servo pressure.